1. Field of the Invention
The present invention relates to a hydraulic controller for a construction machine such as a hydraulic excavator.
2. Description of the Related Art
In hydraulic excavator comprising two series of variable capacity pumps and regulators for each thereof, engine overload is prevented not only by changing the flow rate of the first pump according to the load thereon but also by detecting the load on the second pump, operating the pumps in accordance with each other, and then controlling the total horsepower of the pumps.
There are two cases: the first where working oil from each pump is supplied to each of actuators arranged respectively in two hydraulic systems, and the second where working oil from both pumps is joined together to be supplied such as in the case of a combined operation of the actuators, one case of which being selected appropriately according to actuators to be driven.
To be more concrete, in the case of a raising and rotating operation, the rotation side is supplied with only pressure oil from the second pump, while a boom cylinder is supplied with pressure oil from both pumps.
In the case of a raising and rotating operation, although in the beginning discharge oil from the pumps flows preferentially to the boom cylinder according to load balance, as the rotation comes to a steady state, oil is found to flow only to the rotation side having a lower load thereon. Consequently, due to a shortage of boom raising speed, operators operate a lever, while adjusting so as to match the horsepower of the pumps, to synchronize boom raising speed with rotating speed.
In this case, since the operating speed of multiple actuators cannot be increased at the same time, actuators with higher speeds are to be operated in accordance with the operation of an actuator with the lower speed. Thus, the engine horsepower cannot be fully utilized, resulting in a delay in working cycle time and therefore poor workability.